The present invention relates to an improved double-roll crusher for crushing fatty bones used to obtain rendered bones of low fat content suitable for the production therefrom of gelatin and also glue or animal meal.
Fatty bones are obtained from slaughter houses or as waste from butcher shops. Bones from such sources are often associated with meat and fat. They cannot be used as such for the production of gelatin. Usually they are treated in order to take off the major part of the fat and to obtain the desired granulometry. Most often fatty bones are first sorted to eliminate foreign substances such as pieces of iron or plastic material and they are afterwards sent to a prebreaker and a crusher. The crushed bones are then heated by steam to a temperature of about 90.degree. to 95.degree. C. and charged in a press in order to recover a solid cake consisting largely of bone and a liquid consisting of molten fats, water soluble substances and in some cases bone powder and other proteinous substances. The rendered bones are then dried and introduced into a unit for the preparation of gelatin.
The crushing is intended to reduce bones to a particle size or granulometry suitable for producing gelatin and for obtaining a good separation of noncollagenous proteinous material during the rendering in a press. This granulometry usually ranges between 3 and 18 mm. Furthermore the crushed product must not contain more than a small proportion of powder. This bone powder has a tendency to clog the rendering press and cannot be used for the production of gelatin. Therefore it is necessary to separate the bone powder before the gelatin production step, thereby producing a byproduct which can be used as meat meal, but has a low price because it has a low albumin content. Furthermore, the granulometry must not exceed the highest granulometry acceptable for the acid treatment of the bones in gelatin production. Moreover, since the size of the press outlet is close to the maximum particle size of bones acceptable for the acid treatment in gelatin production, excessively large bone particles are liable to block up the press.